This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to Appln. No. 199 38 274.3 filed in Germany on Aug. 12, 1999; the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The invention relates to a device and to a method for the controlled setting of the gap between the stator arrangement and rotor arrangement of a turbomachine, the stator arrangement of which has a stator carrier and at least one stator segment which is connectable to the stator carrier via at least two holding webs and the rotor arrangement of which provides at least one moving blade row rotatable about an axis of rotation and having a multiplicity of individual moving blades, the moving blade ends of which are located opposite the stator segment and with the latter enclose a radial gap.
2. Description of the Related Art
Turbomachines of the generic type designated above serve primarily, on the one hand, for the controlled compression of gases, as is the case in compressor stages in turbo systems, and, on the other hand, for the controlled expansion of highly compressed and fast-flowing media for driving gas turbines which are used in a way known per se for energy generation. The other aspect of the turbomachine is the increase in their efficiencies and, along with this, a highly efficient conversion of energy by means of the working medium passing through the turbomachine. Loss mechanisms occurring both during the compression of the working media to be compressed and when turbines are being driven are to be reduced or avoided completely by technical means.
In this respect, it is expedient, in particular, to keep the radial gap formed in thermal turbomachines between the rotating and the stationary system components as small as possible, in order to reduce the so-called hydraulic losses which consist of mass flows, albeit small, of the working medium passing through the turbomachine, without at the same time participating in the desired energy conversion. Hydraulic losses thus constitute loss mechanisms which may considerably reduce the efficiency of turbomachines.
The particular problem in the reduction of hydraulic losses is, on the one hand, the need for discrete spacing between the stationary and rotating components of a turbomachine, in order to ensure that the rotor arrangement runs freely; on the other hand, it is expedient, for the reasons mentioned, to keep this interspace as small as humanly possible, this being made more difficult by the criterion that the system components of a turbomachine be capable of expanding under thermal load, with the result that, while a turbomachine is in operation, the relative positions of the individual components change due to a varying thermal expansion behavior. This makes it difficult, moreover, to achieve the least possible gap dimensioning for the entire operating range of a turbomachine which, depending on the type of turbomachine, is exposed to a wide temperature spectrum. Thus, as a result of the centrifugal forces acting on the rotating components, these undergo more rapid expansion, which would basically lead to a reduction of the gap, than the complex thermally insulated components of the stator which experience slower heating and, in a thermally steady operating state, contribute by expansion to an increase in the gap dimension.
Both active and passive measures are known for controlling or influencing the gap dimension, the passive precautions being looked at in more detail below, especially since active control precautions implemented by mechanical setting systems for gap control have high complexity and are suitable only to a limited extent for robust machines subjected to high thermal stress, such as, for example, gas turbine plants.
One possibility for the passive implementation of gap control is the controlled optimization of material combinations with specifically selected coefficients of thermal expansion, which brings about thermal expansion in all the plant components defining the gap, as a result of which the gap, on the one hand, assumes a minimum size and, on the other hand, maintains this minimum gap width over the entire operating range, that is to say temperature range of turbomachines.
Due to the highly complex configuration of known turbomachines, there are very limited possibilities for the choice of any desired material combinations for stator and rotor components in order to improve the thermal behavior. Although the choice of material may be made, taking into account the problem of gap width, it has not been possible hitherto to achieve a satisfactory reduction in the gap dimension simply by the choice of material combination alone.
Another possibility for keeping the gap dimension small is to allow for abrasive surface actions on stator and rotor components. In this case, the mutually opposite surfaces which almost touch one another are provided with abrasive surface coatings which, when the turbomachine is in operation, are stripped off in a controlled manner, by being deliberately ground off or down, and thus lead to an optimized gap.
However, after a single operating cycle of the turbomachine, the gap formed as a result of abrasive action has an optimized maximum gap width which, however, cannot be reduced again.
Finally, design measures for a uniform expansion of the rotor components and stator components of a turbomachine are also possible, but these all entail considerable extra outlay in design terms and, moreover, are not suitable for robust gas turbine use with long-term stability.
The object on which the invention is based is to specify a device for the controlled setting of the gap between the stator arrangement and rotor arrangement of a turbomachine, the stator arrangement of which has a stator carrier and at least one stator segment connectable to the stator carrier via at least two holding webs and the rotor arrangement of which provides at least one moving blade row rotatable about an axis of rotation and having a multiplicity of individual moving blades, the moving blade ends of which are located opposite the stator segment and with the latter enclose a radial gap, and to develop said device in such a way that, irrespective of the operating state of the turbomachine, the gap has the smallest possible gap width which is established without any active regulation. The mechanical design measures to be taken in this case are to be implemented simply and cost-effectively and are to satisfy the requirements for robust use with long-term stability, for example in a gas turbine which is in steady-state operation. Moreover, a method is to be specified, by means of which an optimum reduced gap width setting within a turbomachine between the stator arrangement and rotor arrangement is possible without the use of active control and regulating mechanisms.
The device according to the invention has at least one stator segment, on which are arranged, spaced from one another, two holding webs which engage at least partially into countercontours within the stator carrier. At least one holding web has a holding web portion which engages into the countercontour of the stator carrier and which provides a longitudinal extent, the direction of which limits, with a plane containing the axis of rotation and oriented orthogonally to the radial longitudinal extent of that moving blade which with the stator segment encloses the gap, an angle a to which the following applies:
0xc2x0 less than xcex1 less than 90xc2x0 or
90xc2x0 less than xcex1 less than 180xc2x0.
Due to the inherent heating of the stator segment directly exposed to the hot combustion gases when the turbomachine is in operation, said stator segment experiences a longitudinal expansion which, however, because of the two holding webs engaging into the countercontours of the stator carrier, cannot develop entirely without resistance. The stator segment can nevertheless expand by a specific amount due to t heating and to the given coefficient of thermal expansion. Since the holding web portion running at an inclination is mounted so as to be moveable relative to its countercontour provided in the stator carrier, an elongation of the stator segment parallel to its extent becomes possible. The movement relative to the stator carrier takes place because a different longitudinal expansion of the connected components is established, which is to be attributed to different temperatures and coefficients of expansion.
As a result of the positively guided movement of the holding web portion guided in the countercontour at an inclination to the axis of rotation or at an inclination to a plane containing the axis of rotation, the thermal expansion of material of the stator segment causes the surface of the latter to be spaced from the stator carrier, with the result that the gap dimension between the stator segment and a turbine blade located opposite the latter is reduced. After the appropriate cooling of the plant components, a corresponding reduction in length of the stator segment leads to a reversible movement relative to the stator carrier, this entailing a variation in the gap width.
With the aid of the measure according to the invention, it is possible, by simple design means, to implement a reversible minimum gap width adaption during the entire operation of a turbomachine.
The above-specified angle limitation of between 0xc2x0 less than xcex1 less than 90xc2x0 is to be provided insofar as the stator carrier is capable of expanding more slowly than the stator segment. In the opposite case, in which the stator expands more quickly than the stator segment during transient operating behavior, an angle xcex1 of between 90xc2x0 less than xcex1 less than 180xc2x0 must be selected.